Processes for the co-production of acetic acid and dimethyl ether may be carried out by the catalytic dehydration and hydrolysis of mixtures of methanol and methyl acetate. Such co-production processes are known from, for example WO 2011/027105, WO 2013/124404 and WO 2013/124423.
WO 2011/027105 describes a process for the production of acetic acid and dimethyl ether by contacting methanol and methyl acetate with a catalyst composition at a temperature in the range 140 to 250 C. wherein the catalyst composition contains a zeolite having a 2-dimensional channel system comprising at least one channel which has a 10-membered ring.
WO 2013/124404 describes a process for the co-production of acetic acid and dimethyl ether products from a mixture of methanol and methyl acetate by contacting the mixture at a temperature from 200 to 260 C. with a catalyst composition comprising a zeolite possessing a 2-dimensional channel system comprising at least one channel having a 10-membered ring and a silica:alumina molar ratio of at least 22:1.
WO2013/124423 describes a process for the production of acetic acid and dimethyl ether by contacting a mixture of methanol and methyl acetate with a zeolite catalyst wherein the zeolite has a 2-dimensional channel system comprising at least one channel having a 10-membered ring and having at least 5% of its cation exchange capacity occupied by one or more alkali metal cations.
Co-production processes to produce acetic acid and dimethyl ether from methyl acetate and methanol feed stocks can be represented by equations (1) and (2):CH3COOCH3+H2OCH3COOH+CH3OH  (1)2CH3OHCH3OCH3+H2O  (2)
Sources of methyl acetate suitable for use in such co-production processes may be, for example methyl acetate-containing streams derived from processes for carbonylating dimethyl ether with carbon monoxide in the presence of a carbonylation catalyst to produce methyl acetate. Carbonylation processes of this type are known from, for example U.S. Pat. No. 7,465,822, WO 2008/132441 and WO 2008/132438. However, it has now been found that operation of such processes can result in crude product streams which are sub-optimal for direct utilisation in co-production processes of the type described above and in particular, those crude product streams which comprise significant amounts of dimethyl ether, such as crude product streams formed in carbonylation processes operated under low carbon monoxide partial pressure conditions.
Furthermore, direct utilisation of crude methyl acetate feed streams containing fairly high levels of dimethyl ether in co-production processes of the type described above has been found to inhibit the formation of dimethyl ether product and/or acetic acid product. This disadvantage may be further exacerbated by the use of commercial methanol sources which typically contain dimethyl ether and in amounts which may be in excess of 25 mol %.